The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of one or more of the presently named inventors, to the extent such work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Various wireless standards, such as WI-FI, may operate on multiple radio-frequency (RF) bands. For example, Standard 802.11n-2009 by the Institute of Electrical and Electronics Engineers (IEEE) may be used in the 2.4 gigahertz (GHz) band or the 5 GHz band. This may require multi-band transceivers or other components of a radio.
A second harmonic is a form of non-linearity that is located substantially at twice the fundamental frequency of a desired signal. Second harmonics may be present in various amplifiers, e.g., power amplifiers in wireless-communication transceivers or power amplifiers.
For a wireless transmitter, governmental and international regulations may specify the maximum permissible emissions in selected frequency bands. Second harmonics may be the strongest distortion tone from a transmitter. Some prior schemes use filters at the frequency of the second harmonic. However, a disadvantage of this approach is that the filters may increase the insertion loss and reduce the power efficiency of the transmitter. Filters may also increase the physical size of the radio and thus the size of components incorporating the radio, e.g., cellular telephones or wireless-network adapters.